const Koa = require('koa')
const app = new Koa()
let m1 = function(ctx,next){
    next()
}
let m2 = function(ctx,next){
    next()
}
app.use(m1)
app.use(m2)

app.use(ctx =>{
    cxt.body = 'hello'
})
/*
    中间件使用的时洋葱的执行机制
*/ 